Different behavioral mechanisms underlie tolerance to the anorectic effects of fenfluramine and quipazine

Chronic administration of fenfluramine or quipazine in rats before scheduled daily feeding sessions led to rapid and complete tolerance to the initial anorexia. Daily injections of fenfluramine after the daily meal also led to full tolerance. Quipazine administration after meals led to the development of little tolerance, indicating that quipazine tolerance appears to be learned or contingent. The implications of these data for neurochemical mechanisms of satiety are discussed.